The present invention relates, in general, to a light sensing device and is more particularly concerned with a light level indicator but provides a "go-no-go" condition. This condition may be indicated by a pair of indicator lights, one of which is red and the other of which is green and which are illuminated in a mutually exclusive manner to indicate whether the sensed light is above or below a predetermined threshold level.
With the passage of new federal legislation concerned with safety in many different areas, there has developed a need for devices that can sense predetermined light levels to determine if these levels are sufficiently high for proper working conditions. For example, in the mining area such as in the mining of coal, there is now a requirement that a predetermined light level be maintained in the mines. Some devices do exist for measuring light levels, of course, but these devices use a meter and thus are relatively complex. Furthermore, even though the law does require predetermined light level to be maintained these levels in a mine, for example, are still not that bright and thus with a meter instrument it is difficult to take an accurate reading. Another problem associated with known devices is that they usually require that a number of readings be taken in a particular area to obtain an accurate indication. These readings are then averaged which makes the operation rather time consuming.
Accordingly, one object of the present invention is to provide a light sensing device that is very simple to use and that does not require the reading of a meter. In accordance with the present invention the indicator device is a "go-no-go" type device that includes at least one indicator light for indicating whether the sensed light is not of a sufficient level as required.
Another object of the present invention is to provide a light level indicator that has an adjustable threshold level. In accordance with the present invention a multi-position switch is used for setting the threshold at one of a number of different levels. In this way the illumination to be measured in a particular area can be determined within the range of settings of the switch.
A further object of the present invention is to provide a level indicator that comprises two light sensing elements, one of which measures a direct light and the other of which measures reflected light from a relatively large surface.
Still another object of the present invention is to provide an adapter for the light level indicator of this invention which adapter comprises a radioactive source for checking the calibration of the device.